The subject invention is directed toward the valve art and, more particularly, to an improved air operated diaphragm valve.
The valve is particularly suited for use as a shut-off valve for high pressure, toxic gases as used in the semi-conductor industry and will be described with reference thereto; however, as will become apparent, the valve could be used in other environments for other purposes.
The high pressure and toxic gases used as process gases in the semi-conductor industry require highly reliable valves. Reliability is measured by the ability to contain the system fluid and shut off the flow of the fluid. The semi-conductor industry has chosen packless (metal membrane) valves to provide the desired level of reliability and safety. Currently diaphragm type packless valves are preferred because they are easier to clean and faster to purge due to their lower internal volume (compared to bellows valves).
The size of the diaphragm needed is controlled by the flow and cycle life requirements of the valve. In a high pressure system, the size of diaphragm needed requires a large amount of force to overcome the pressure load of the system fluid on the diaphragm. In the majority of applications for the subject valve, the operator must produce this large force while remaining within limitations on the size of the package and the pressure available to actuate the operator. In order to meet all of these requirements, some type of force multiplying mechanism is needed between the valve element and operator.
Precise control of the force output of the operator is needed. If the force output is too low, the operator will not be able to overcome the pressure load on the diaphragm and shut off the flow. If the force output is too high, the valve may not open with the pressure available to actuate the valve.
To produce high reliability, precise control of the up and down stroke movement of the diaphragm is needed. In the case where a deformable seat material is used, good containment of the material is needed to minimize deformation that would result in increased diaphragm movement, which would decrease cycle life.
Because of the above-noted factors, there is an ongoing need to improve the valves and to increase seat and diaphragm life through better control and design of the relationships between the various components including the force multiplying mechanism and the stroke adjustment mechanism.